Using the Cusp to Study Magnetic Reconnection

1
Using the Cusp to Study Magnetic Reconnection

• K.J. Trattner
• Lockheed Martin Advanced Technology Center
• Palo Alto, CA, USA

2
The Principal Regions of the Magnetosphere and
Boundaries
3
Outline

• The Cusp
• Cusp Structures
• - Temporal Cusp Structures
• - Spatial Cusp Structures
• The Location of the Reconnection Line
• Summary and Conclusion

4
Reconnection with Southward IMF
CONVECTION
Lockwood 1995
5
Plasma Entry
Precipitating ions in the cusp Reiff et al.,
1977 Escoubet et al., 1997
Magnetopause
Fast Particle
Slow Particle
Magnetospheric Cusp
Solar Wind
Precipitating cusp ions experience a velocity
filter effect with lower energies convecting
further poleward Rosenbauer et al., 1975
Shelley et al., 1976
6
Cusp Ion Energy Dispersion for Southward IMF
Velocity Filter Effect Decreasing Ion Energy
with Increasing Latitude
7
Multiple Cusps during one Pass!
Triple Cusp Temporal or Spatial Effect?
8
Temporal Is the reconnection rate variable or
does it even stop?Spatial Are there multiple
reconnection lines?

• How do we distinguish between temporal and
  spatial Effects?

9
Poleward Convecting Structures
Svalbard Radar Observations Poleward Convecting
Structures as Signatures for Variations of the
Reconnection Rate at the Magnetopause.
Cluster Ions and Electrons Observations of
Transients in the vicinity of the Magnetopause.
Lockwood et al. 2001
10
Temporal Cusp Structures Different
Satellites Observe Changing Cusp Profiles.
e.g., Lockwood et al., 1995, 1997..
11
Important Parameter for Temporal Cusp Structures
when observed with Satellites at different
Altitudes The Velocity of convecting
Structures relative to the Satellite Velocity
12
Low Altitude FAST Satellite is overtaking a
convecting Cusp Structure Satellite Encounters
a Step-Down Cusp Structure Mid Altitude
POLAR Satellite is overtaken by a convecting Cusp
Structure Satellite Encounters a Step-Up Cusp
Structure.
13
Onsager et al. 1995
Low-Altitude Satellite
Two similar Step-up Cusp Structures observed 20
min apart.
High-Altitude Satellite
14
Spatial Cusp Structures
Spatially Separated Flux Tubes from two
Reconnection Lines at the Magnetopause.
Neighboring Field Lines on both sides of the Flux
Tubes have Different Time Histories since
Reconnection.
15
Low- and High Altitude Cusp Observations
FAST Cusp Pass 3 Minutes Polar Cusp Pass 20
Minutes
16
Low- and High Altitude Cusp Observations
FAST Cusp Pass 3 Minutes Polar Cusp Pass 5
hours Same Overall Structure as seen by FAST with
22 smaller steps related to variations in the
reconnection rate
Trattner et al. 2002a
17
Cluster/CIS Ion Energy Dispersions
Double Cusp Spatial or Temporal Structures?
All satellites at the same altitude. Can not
distinguish between temporal and spatial Effects.
18
Cluster 1 and 4 have entered the cusp and
encounter downward precipitating ions (the first
set of the cusp structures).
19
Cluster 1 and 4 have crossed into the other
convection cell. At the same time they
encountered the second set of cusp
structures. SPATIAL CUSP EVENT!
20
(No Transcript)
21
Cluster/CIS Ion Energy Dispersion
Double Cusp Spatial or Temporal?
22
Cluster 1 and 4 encounter the second set of cusp
structures at different time and
latitudes. TEMPORAL CUSP STRUCTURES!!!
23
(No Transcript)
24
Where Does Reconnection Occur at the Magnetopause?
25
Large Scale Reconnection GeometrySouthward IMF
Two ModelsAnti-Parallel vs. Tilted X Line
Reconnection
Gosling et al. (1991) Cowley
(1976) Fuselier et al. (2002)
26
Ion Jets observed at the Magnetopause
Phan et al. 2000
27
Precipitation is Different for the Two Types of
Reconnection
Anti-Parallel Tilted Line The
Key Difference is The Flux Near Noon
28
IMAGE Distinguishes Anti-Parallel and Component
Reconnection
View from Sun
View from Sun
Tilted Neutral Line
Anti-Parallel
30 December 2001 220806 UT
IMAGE SI12 Proton Aurora
Neutral Line Mapped to the Ionosphere
Noontime Gap
Continuous Across Noon
Noontime Gap Anti-Parallel Reconnection
29
Is This the End of Component Reconnection?
Another Event
View from Sun
View from Sun
Tilted Neutral Line
Anti-Parallel
11 January 2002 065800 UT
IMAGE SI12 Proton Aurora
Neutral Line Mapped to the Ionosphere
Noontime Gap
Continuous Across Noon
No Noontime Gap Component Reconnection
30
Does Reconnection Turn Off When the IMF Rotates?
Reconnection is continuous, even when the IMF is
changing IMF change gtgtgtgt Simple change in the
location
31
Ion Dispersion in the Cusp Distance to the
Reconnection SiteOnsager et al. 1990, Fuselier
et al. 2000, Trattner et al. 2004
Assumes Instantaneous acceleration
Simple Field Line Structure
32
Polar/TIMAS Cusp CrossingNorthern Hemisphere
Cusp Open Field Line Region Closed

Field
Lines
2-Year Study 102 Cusp crossings
B(z) lt 0 all clock angles
- Limited to small B(x) cases
33
Polar/TIMAS 3D Plasma Measurements
Precipitating Ions Mirrored Ions
Mirrored Precipitating
Mirrored Precipitating
Vm Ve
34
Anti-Parallel Reconnection (MLT 1510) March 4,
1998 Clock Angle 191

• MP Shear Angles
• RED antiparallel
• BLACK parallel
• WHITE in RED
• within 3 of anti-

Black Circle Terminator
MP Share Angle Calculation based on T96 and
Cooling et al. (2001)
35
Anti-Parallel Reconnection (MLT 1025) November
6, 1997 Clock Angle 195
36
Summer Crossing Component Reconnection and
Maximum Dayside Shear

• View from the Sun
• Black circle - terminator
• Color MP shear
• black parallel
• red anti-parallel
• White lines in red
• regions
• anti-parallel reconnection
• White line through sub-
• solar point
• Tilted neutral line line
• through subsolar region
• that follows maximum
• perpendicular component Cowley 1976,
• Moore et al. 2002

Nominal dynamic pressure
Dayside reconnection follows locus of maximum
shear
37
Winter Crossing Dipole Tilt Effect
Dipole tilt effect Winter moves the locus of
maximum shear above the GSM
equator Reconnection line follows this change
Locus of maximum shear
38
Equinox Crossing Tilted Neutral Line and
Maximum Shear Line Coincide
Reconnection follows maximum shear but both
maximum shear and the tilted neutral line
coincide
Small Bx
39
Bx Effect Anti-Parallel Reconnection for Large
Bx
When Bx becomes large (Bx/Bo 0.7),
Reconnection becomes anti- parallel (no
longer follows region of maximum shear on
the dayside) This also happens when Bz becomes
dominant (cant distinguish component
and anti-parallel sites)
Large Bx
40
Summary

• Cusp Structures are the result of crossing into
  spatially separated flux tubes.
• Cusp Structures are the result of temporal
  convecting flux tubes.
• Anti-Parallel Reconnection Location for Clock
  Angles of 20 30 from Southward IMF
• Tilted X-Line Reconnection Location for Larger
  Deviations from Southward IMF
• Seasonal Effects for Tilted X-Line
• BX effect Large BX anti-parallel reconnection